Try to salvage the relationship;
Ask the shop owner for a progress bill to see what portion of the job has been completed?
Ask the shop owner how many more weeks complete the car?
Ask the shop owner how much more money it will cost you to complete the car?
Based on the answers, decide to continue the relationship or pick up the car and take somewhere else.
Remember, you are relying on the shop to stand by their work in the future. If you turn the relationship into an adversarial one you will regret it for as long as you own the car.
Keith